
I tried to make my own sprite from scratch. I'm not sure if it succeeded, so here the points I tried to consider:
* Silhouette: In your reference the ultramarine is divided in two parts: upper and lower part. The upper part is mainly one big closed shape and the lower parts contains two legs (skinny thights and thick feet). Yours is not seperated enough, just one big blob instead of one with two legs (mostly because of the black shadow).
* Details vs. Flat areas: Your version lacks in simplicity. Often the pixel are obscure, it's unclear if it's a detail or a shading of a otherwise flat area.
If you are unsure what I did, please ask, I'll try to elaborate.